In-Game Description

A sorcery superior to Magic Weapon.
Reinforces weapon in other hand with intense magic,
allowing for infliction of heavy magic damage.

The old purists of the Melfian Magic Academy
view swordplay as a barbaric form of engagement.

Use

Increases weapon's Magic damage by [(Weapon's original Magic damage + 50) x 1.2]. Duration depends on Intelligence.
Based on some testing done and posted here, it is clear that the above formula is wrong. However, great magic weapon was not specifically tested. If the formula follows the pattern, we can infer that the bonus given by this spell is most likely [(total base damage * 0.2) +5]